Influence of Pressurization Rate and Pressure Pulsing on the Inactivation of Bacillus amyloliquefaciens Spores during Pressure-Assisted Thermal Processing

Abstract

Pressure-assisted thermal processing (PATP) is an emerging sterilization technology in which a combination of pressure (500 to 700 MPa) and temperature (90 to 120 degrees C) are used to inactivate bacterial spores. The objective of this study was to examine the role of pressurization rate and pressure pulsing in enhancing PATP lethality to the bacterial spore. Bacillus amyloliquefaciens TMW 2.479 spore suspensions were prepared in deionized water at three inoculum levels (1.1 x 10(9), 1.4 x 10(8), and 1.3 x 10(6) CFU/ml), treated at two pressurization rates (18.06 and 3.75 MPa/s), and held at 600 MPa and 105 degrees C for 0, 0.5, 1, 2, 3, and 5 min. Experiments were carried out using custom-fabricated, high-pressure microbial kinetic testing equipment. Single and double pulses with equivalent pressure-holding times (1 to 3 min) were investigated by using the spore suspension containing 1.4 x 10(8) CFU/ml. Spore survivors were enumerated by pour plating, using Trypticase soy agar after incubation at 32 degrees C for 2 days. During short pressure-holding times (< or = 2 min), PATP treatment with the slow pressurization rate provided enhanced spore reduction over that of the fast pressurization rate. However, these differences diminished with extended pressure-holding times. After a 5-min pressure-holding time, B. amyloliquefaciens population decreased about 6 log CFU/ml, regardless of pressurization rate and inoculum level. Double-pulse treatment enhanced PATP spore lethality by approximately 2.4 to 4 log CFU/ml, in comparison to single pulse for a given pressure-holding time. In conclusion, pressure pulsing considerably increases the efficacy of PATP treatment against bacterial spores. Contribution of pressurization rate to PATP spore lethality varies with duration of pressure holding.

Use of Pressure for Improving Storage Quality of Fresh-Cut Produce

“…When these bacteria were subjected to 600 MPa at 60 ı C for 10 min, the population (5.1 log CFU ml 1 ) decreased to non-detectable levels (data not shown). This result was in confirmation of other reports on effect of HP in combination with heat (95-105 ı C) on inactivation of spores of B. stearothermophilus (Furukawa and Hayakawa 2000) and B. amyloliquefaciens (Ratphitagsanti et al 2009), although mild pressure treatments (60 MPa at 40 ı C) induced spore germination of Bacillus spp. through activation of the spore's nutrient receptors (Shigeta et al 2007).…”

Effect of compression and decompression rates during high hydrostatic pressure processing on inactivation kinetics of bacterial spores at different temperatures

“…For the SS treatment, a proportion of 15% germinated spores could be detected, which confirms that these treatment conditions would be the most lethal for an industrial scale HHP process. Similar findings were reported by Ratphitagsanti et al (2008), who worked with Bacillus amyloliquefaciens spores at 90e120 C. They reported that for short pressure holding times (<2 min), HHP treatment with the slow pressurization rate provided enhanced spore reduction, however, these differences diminished with the longer holding times. This behavior of spores during a slow pressurization could be explained by a pressure induced non-nutrient germination, in which the germination receptors are triggered at pressures between 200 and 500 MPa (Wuytack et al, 1998).…”

“…However, variation in come up time may affect the inactivation kinetics of microorganisms (Ratphitagsanti, Ahn, Balasubramaniam, & Yousef, 2008). Therefore, consistency and awareness of pressurization and depressurization rates are important in process development.…”

High-Pressure Processing Technologies for the Pasteurization and Sterilization of Foods

“…Immediately available to commercialize PATP technology, is alternative (c) in Table 2, i.e., temperatures above 100°C to inactivate bacterial spores in a reasonably short time. The limitation of this alternative is the need for research on reaction kinetics in the pressure and temperature range required for this alternative, a severe limitation at this time (Ramírez and Torres 2009;Torres et al 2009b;Martínez Monteagudo et al 2011;Valdez-Fragoso et al 2010) when compared to the large availability of data on the inactivation of bacterial spores (Reddy et al 2003;Margosch et al 2004Margosch et al , 2006aRajan et al 2006;Ahn et al 2007a,b;Paredes-Sabja et al 2007;Naim et al 2008;Zhu et al 2008;Juliano et al 2009;Ratphitagsanti et al 2009). …”